A high-resolution near infrared spectrum of the CrCl radical has been recorded in thermal emission with Fourier transform techniques in the interval from 6 900 cm−1 to 11 500 cm−1. Two dominating band systems have been found in this region; (1) The A 6Σ+→X 6Σ+ system, analyzed in the present work, consisting of the (0,0), (0,1), (1,0), (2,0), and (3,0) bands, the (0,0) band being located at around 9450 cm−1; (2) the B 6Π→X 6Σ+ system, with a band interpreted as (0,0), located between 8700 cm−1 and 9000 cm−1, overlapping the (0,1) band of the A 6Σ→X 6Σ+ system. A rotational analysis of the A 6Σ+→X 6Σ+ system has been carried out, and the following principal parameters (cm−1) have been derived: X 6Σ+: ωe=396.6621, Be=0.167 587 3, De=1.1835⋅10−7; A 6Σ+: ωe=379.39, Be=0.156 51. Local perturbations in the A 6Σ+ (v=0,1) levels have been attributed to interactions with the B 6Π (v=1,2) levels. In the present work, we have constrained the investigations on the B 6Π→X 6Σ+ system to the verification that the lower state is indeed X 6Σ+. This verification has been achieved through successful matchings of branches in that system to known combination differences of X 6Σ+. The assignment of the upper state as B 6Π is based on the characteristic appearance of the band. Ligand field and density functional calculations have been performed on CrF and CrCl. The results from these calculations indicate that the approximate structure of the B 6Π and 1 6Δ excited states of CrF and CrCl is Cr+[3d44s(6D)]X−, while for the X 6Σ+ ground state in both molecules it is Cr+[3d44s(6D)∼3d5(6S)]X−. A combined DFT/LFT treatment has been carried out on the Cr+ 3d5and 3d44s configurations of both molecules in order to calculate the location of the A 6Σ+ state and of a number of low-lying states in the quartet manifold.

Articles you may be interested inElectronic properties of CrF and CrCl in the X 6 Σ + state: Observation of the halogen hyperfine structure by Fourier transform microwave spectroscopy

The B 6Π–X 6Σ+ band system of the CrF radical has been recorded in emission with FTS techniques in the region between 6965 and 9240 cm−1, using a resolution of 0.025 cm−1. A rotational analysis including the (0,0), (1,1), (1,0), (0,1) and (1,2) bands of this system has been carried out, and a set of molecular parameters has been derived for the B 6Π state. The present analysis has also resulted in substantially better determined values for the λ and γ parameters of the X 6Σ+ ground state. An improved set of molecular parameters has been derived for the previously analyzed, heavily perturbed A 6Σ+ state. The present analysis gives strong support for the interpretation that the local perturbations in the v=0–3 levels of A 6Σ+ are due to interactions with the vibrational levels v=3–6 of the B 6Π state. Earlier suggestions involving a low-lying 4Π state as the dominating perturber of the A 6Σ+ state must now be considered as erroneous. A previously suggested interpretation of the 7400 cm−1 band as being possibly due to a quartet transition has also been shown to be in error. The derived first order spin-orbit parameter value of B 6Π [A=47.0382(18) cm−1] and the equilibrium bond distances of X 6Σ+ [1.7839 Å], A 6Σ+ [1.8919 Å], and B 6Π [1.8277 Å] have been discussed, and it has been proposed that the 9σ (Cr4s–4p) molecular orbital of CrF is slightly bonding, while 4π (Cr3dπ) is nonbonding and 10σ (Cr3dσ) antibonding.

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